Means for synchronizing motors.



I No. 7l5,0l9. Patented Dec. 2, I902. F. E. CASE.

MEANS FOR SYNCHRONIZING MOTORS.

(Applipation filed Feb. 11. 1899.)

(No Model.)

WITNESSES. INVENTEIR. d wfd tw Frank 156a.

UNrTan STATES PATENT FFIQE.

FRANK E. CASE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO THE GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEIV YORK.

MEANS FOR SYNCHRONIZING MOTORS.

SPECIFICATION forming part of Letters Patent No. 715,019, dated December2, 1902.

Application filed February 11, 1899. Serial No. 705,301. (No model.)

T0 (0 whom it may concern.-

Be it known that I, FRANK E. CASE, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Means for SynchronizingMotors, (Case No. 777,) of which the following is a specification.

My present invention has for its object to provide a means forequalizing the action of electric motors when connected in series. It iswell known that when two electric motors are connected in series theyshould for best results be geared to the same load, as if one runsfaster than its normal rate it tends to stop the other. For example,when two motors connected in series are geared to different axles of arailroad-car if one of them slips and then speeds up its counterelectromotive force rises to such a degree that the torque of the othermotor is materially reduced, and as the slipping motor exertspractically no useful effect the car tends to stop entirely. It is thennecessary to cut in resistance until the speed of the slipping motor isreduced to that corresponding to the speed of the car, when it willcatch, an operation causing some considerable delay and annoyance. Thisaction is particularly troublesome in wet weather, when it sometimesrenders the main tenance of schedule time impossible. I obviate thetrouble by connecting in a shunt around each motor a device which whenthe motor slips and its counter electromotive force runs up closes acircuit around the slipping motor, so that current may flow to the othermotor in a measure independently of the current-flow in the circuit ofthe slipping or racing motor.

The improvement, therefore, in the art of regulating electric motorswhich I have devised consists in one aspect of thus establishing acurrent path around the slipping motor whenever its counterelectromotive force runs up, which tends to weaken the torque of theslipping motor, as well as to strengthen the torque of the other motor.The specific mechanism which I have devised for this purpose consists ofapair of electromagnets connected in series around the two motors with alead from the wire between the magnets to a point between the motors.These magnets are balanced in their action so long as the drop aroundthe two motors or current-flowin them is equal. An armature under theinfluence of the magnets controls a switch, which when thrown to oneside or to the other establishes a new current-path around one or theother of the two motors. The current-path preferably includes a moderateresistance, for reasons presently to be explained. I take thisdescription of the device as typical of any whichmay be devisedembodying my invention.

The accompanying drawing is a diagram showing the invention in one formwhich it may take, in which the particular mechanism just brieflydescribed is employed; but of course many other means might be used tocarry out the method.

In the drawing, T is the trolley, R is the resistance, M M are themotors, and G is the ground-wire.

I do not show any special means of regulating the motors in the ordinarysense of the term, because any controlling device whatever may beemployedas, for example, a series parallel controller.

A is the device embodying my invention, consisting of the balancedmagnets A A 111 a circuit around the motors with a lead B from a pointbetween them to a point between the motors. The switch-blade A iscontrolled by the action of the magnets and reciprocates betweencontacts a a in circuit, respectively, with the resistance R R Thewinding of the magnets is of high resistance, as it must exhaust theentire potential across the circuit without taking an unreasonably largecurrent.

The action of the device is as follows: Assume, for instance, that motorM races and its counter electromotive force rises, so that the currentin the circuit of the two motors is out down and the torque of themotorM falls off. Under these conditions the drop around the motor Mwill be so great that the magnet A will overpower the magnet A and drawup the armature,throwing the switch A to the dotted-line position, thusestablishing a circuit by way of the resistance R, contact a, and lead Bto the terminal of the motor M The resistance It acts to steady themotor against the sudden rise of potential and prevents a jerky action.Owing to the resistance and counter electromotive force of the motor Mthe greater part of the current will be diverted around it to the motorM the torque of the motor M will be greatly cut down, and the torque ofthe motor M increased. Under these conditions the motor M' will slowdown until the wheel which it drives again adheres to the track. Whenthe motors are again in step, so to speak, the magnets A A will bebalanced and the switch will open. Theoretically, as soon as theswitch-blade touches the contact ct the magnet A is short-circuited; butowing to the high-resistance winding it takes a short time for itsmagnetomotive force to run down, the action being thus prolonged for amoment. In practice the switch-blade A will vibrate from one contact tothe other in accordance with the relative speed of the motors M M N0difliculty occurs on account of sparking at these contacts, inasmuch asonly half the line-voltage is broken at them at any time; but as anadditional precaution I may make the contacts a {L2 of carbon and, ifpreferred, any usualorsuitablearc-extinguishing means, such as ablow-out magnet, may also be employed. The springs S S are used toprevent the action from being produced by mere accidental differences inthe counter electromotive forces of the two motors, such as might beproduced by differences in their characteristic curves.

My invention is in no manner limited to two motors, though it will bemost generally thus applied. Its application to other numbers ofmachines is apparent and requires no illustration or description.

I do not claim in this application the method disclosed herein, since itconstitutes the subject-matter of a divisional application, Serial No.103,092, filed April 16, 1902.

Having thus described myinvention, what I claim as new, and desire tosecure by Letters Patent of the United States, is

1. The combination of motors in series with means actuated by anincrease in electromotive force of any motor above that of others, fordiverting current from such motor to the other or others.

2. The combination of motors in series,with means for shunting as awhole any motor which tends to slip, and means operating on the slippingof said motor for actuating said shunting means.

3. The combination of motorsin series,with means for closing ashunt-path around any motor which tends to slip and thus increasing thecurrent in the non-slipping motor or motors, and means operating uponthe slipping of said motor for actuating said shunting means.

4. The combination of motors in series,with an electromagnetic switchacting automatically to shunt any motor which tends to slip.

5. The combination of two motors in series, with anelectromagnetically-operated switch having windings in shunt to eachmotor, the two windings being opposed in eifect so that when thecurrent-flow in the two motors is equal, the switch is in a neutralposition, with contacts upon the switch for closing a shunt-path aroundeither motor; whereby when the drop around one motor exceeds that aroundthe other, the switch will be actuated to close a shunt-path around themotor the circuit of which has the greater drop.

6. The combination of a pair of motors driving a common load but notmechanically geared together, with means for increasing the torque ofone of the motors when the other tends to slip.

7. The combination of a pair of motors driving a common load but sogeared that one or the other of the motors may slip or race, with anelectromagnetically-operated switch automatically acting to divertcurrent from the slipping motor to the circuit of the motor at normalspeed.

8. The combination of motors in series,with an electromagnetic switchact-ing automatically to shunt any motor which tends to slip and meansfor preventing the action from taking place by mere accidentaldifference of counter electromotive force.

In witness whereof I have hereunto set my hand this 10th day ofFebruary, 1899.

FRANK E. CASE.

Witnesses:

B. B. HULL, EDWARD IVILLIAM, Jr.

